Electrical heating unit

ABSTRACT

An electrical heating unit including a plate or panel of a glassy material having in intimate physical contact with a surface of the plate, in a selected area of the plate surface, a 240 volt heating element comprising a pair of electrical resistance conductors extending in sinuous parallel paths over the contacted area of the panel surface, and circuit means for normally connecting the conductors across opposite terminals of a 240 volt source of electrical energy with two sets of temperature responsive contacts included in the circuit means for interrupting electrical energy to the conductors when the temperature of the heating unit reaches a preselected maximum temperature.

United States Patent [191 Hocker ELECTRICAL HEATING UNIT [75] Inventor:James P. Hocker, Corning, NY.

[73] Assignee: Corning Glass Works, Corning,

22 Filed: Sept. 24, 1973 21 Appl. No.: 400,216

[52] US. Cl 219/543, 219/452, 219/464,

219/522, 174/685, 338/61, 338/308 [51] Int. Cl. H05b 3/16, H05b 3/74[58] Field of Search 219/230, 211, 212, 213,

3,496,336 2/1970 Hingorany et a1. 219/464 3,668,367 6/1972 Williams219/212 3,757,087 9/1973 Bernard 219/549 3,758,747 9/1973 Rohr 219/212Primary Examiner-Volodymyr Y. Mayewsky Attorney, Agent, or FirmCharlesW. Gregg; Clarence R. Patty, Jr.

[57] ABSTRACT An electrical heating unit including a plate or panel of aglassy material having in intimate physical contact with a surface ofthe plate, in a selected area of the plate surface, a 240 volt heatingelement comprising a pair of electrical resistance conductors extendingin sinuous parallel paths over the contacted area of the panel surface,and circuit means for normally connecting the conductors across oppositeterminals of a 240 volt source of electrical energy with two sets oftemperature responsive contacts included in the circuit means forinterrupting electrical energy to the conductors when the temperature ofthe heating unit reaches a preselected maximum temperature.

6 Claims, 1 Drawing Figure PATENTEDHDV 5 1914 m l m mh T 1 ELECTRICALHEATING UNIT BACKGROUND OF THE INVENTION In an electrically heatedappliance employing a heating unit comprising a panel or plate of aglassy material having heating elements including narrow continuousstrips of electrical resistance heating conductors in intimate physicalcontact with or integrally bonded to an area of one of the surfaces ofthe panel of the heating unit, electrical leakage can occur through thematerial of such a panel at certain times such as when the temperatureof the panel exceeds by a selected allowed margin, a normal maximumoperating temperature for such panel. Such electrical leakage can, whenoverly large, present the possibility of an electrical shock. Forexample, kitchen ranges having smooth continuous cooktops made of aglassy material, such as a glassceramic material, are becomingincreasingly popular. The cooktop of such a range comprises a panel ofsaid glassy material which may be the panel of a heating unit such asthat discussed above. In actuality, such a panel usually provides fortwo or more of said heating units, each such unit including a selectedarea of the panel to be used as a heating area on the upper surface ofthe panel. As mentioned above, electrical leakage through the materialof such a cooktop can present the possibility of an electrical shock.For example, a housewife handling an electrically conductive cookingvessel in contact or resting on a cooktop cooking surface of the typementioned, is subject to a possible electric shock if an overly largeelectrical leakage such as that mentioned occurs. This is especiallytrue, of course, if the housewife handling the vessel is also in goodcontact with an electrical ground such as an electrically conductivepart of the cooking range itself or any other electrically conductiveand electrically grounded item in the immediate environs of the range.Accordingly, it is an object of the present invention to provideelectrical heating units of the class mentioned using 240 volt heatingelements and which include, to the extent possible, a reduction in thepossibility of an electrical shock due to an inadvertent electricalleakage occurring from overheating of the glassy material of the panelsused in the heating units.

Other objects and characteristic features of the invention will becomeapparent as the description proceeds.

SUMMARY OF THE INVENTION The invention is believed to be adequatelysummarized in the foregoing abstract of the disclosure and, therefore,for the sake of brevity and to prevent repetition and redundancy to theextent possible, no further summary of the invention will be given noris any considered to be necessary.

BRIEF DESCRIPTION OF THE DRAWING The single drawing FIGURE comprises abottom plan view of an electrical heating unit embodying the invention,such view including electrical circuit means for energizing such unitfrom a suitable source of electrical energy.

PREFERRED EMBODIMENT OF THE INVENTION Referring to single drawing FIGUREin detail, there is shown a surface 11 of an area 12 of a plate or panel10 of a glassy material and which may, for example, be an area of thelower surface of a smooth glass-ceramic cook-top of a kitchen range suchas previously discussed. A 240 volt heating element 13 comprises a pairof first and second suitable electrical resistance conductors l4 and 15which extend parallel with or adjacent to each other in sinuous,winding, serpentine or back-and-forth parallel paths over part ofsurface 1] of area 12 of panel 10, such conductors l4 and 15 being inintimate physical contact or made to be integral with said part ofsurface 11. Conductors 14 and 15 may, for example, comprise narrowcontinuous strips of a conductive film bonded to the surface of saidpart of area 12 as disclosed in US. Pat. No. 3,067,315, issued Dec. 4,1962, to Bohdan Hurko, or the conductors l4 and 15 may be cut from arelatively thin foil of an electrical resistance heating material andsecured to said part of surface 11 by a suitable adhesive or cement.However, it is pointed out that conductors 14 and 15 need notnecessarily be a conductive film or foil but may be electricalresistance ribbons or wires which are held against said surface 11 inany suitable manner such as being so held by a suitable backing sheet ofa heat resistant and electrically non-conductive material, as is wellknown in the art.

A first electrical circuit arrangement or circuit means, comprisingwires 16 and 18 connects first extreme opposite ends 14a and 15b ofconductors l4 and 15, respectively, with each other and, over a wire 20,with a fixed contact member a of a set a-b of normally closedtemperature actuated or responsive contacts of a thermostat or thermallysensitive switch T, the movable contact member b of said set of contactsa-b being shown connected over a wire 22 with the negative terminal of acommercial 240 source PS of alternating electrical current having aneutral terminal N connected to ground. A second electrical circuitarrangement or circuit means, comprising wires 17 and 19, connectssecond extreme opposite ends 1412 and 15a of conductors l4 and 15,respectively, with each other and, over a wire 21, with a movablecontact member :1 of a set c-d of normally closed temperature actuatedor responsive contacts of said thermostat or thermally sensitive switchT. The fixed contact member c of said set of contacts c-d is shownconnected over a wire 23 with the alternatingly positive terminal ofsaid source PS of electrical current.

Thermostat or switch T does not, per se, form part of the presentinvention but such switch may, for example, be any of the well knowntypes of thermostats or switches which include sets of temperatureactuated contacts, such as contacts a-b, and c-d in the drawing, whichnormally occupy or are in a closed condition or position for completingan electrical circuit therethrough and which are actuated to an open orcircuit interrupting position or condition when a temperature sensed bythe thermostat or switch T reaches a preselected maximum temperature. Itwill be understood by those skilled in the art that a thermostat such asT is intended to actuate its sets of contacts a-b and c-d to openconditions when the temperature of area 12 of panel 20, for example,reaches a preselected maximum normal temperature, that is, a maximumtemperature reached under normal operating conditions.

The positive and negative numerical values or designations shown onconductors 14 and 15 represent one set of instantaneous values ofvoltage potentials in the approximate regions of the conductors-wherethe numerical values are shown, when the heating element 13 is connectedwith the source PS of alternating current as hereinbefore described. Thevalues of voltage potential in the lengths of the conductors between theregions indicated by said numerical values increase or decrease inaccordance with the directions of movement along said lengths, as willbe readily apparent from a brief glance at the drawing by those skilledin the art. It is pointed out that electrical leakage through thematerial of the panels 12 is effectively cancelled out due to theopposite polarities of the parallel paths of conductors 14 and 15 asdiscussed below.

OPERATIONAL EXAMPLE OF THE INVENTION There will now be set forth a briefoperational example of the manner in which the invention disclosedreduces the possibility of electrical shock when electrical leakagethrough the material of a panel such as is overly large.

Referring to the drawing, it will be assumed that ends 140 and b ofconductors l4 and 15 are connected with each other and to thealternatingly negative terminal of source PS as shown and as previouslydiscussed, and that ends 14b and 15a of the conductors are connectedwith each other and to the alternatingly positive terminal of source PSas also shown in the drawing and previously discussed. Consider, forexample, electrical leakage occurring in area 12 of panel 10 in theregion generally designated by the letter L in the drawing, any part ofsuch leakage which is not cancelled out by flowing generallyhorizontally through the material of panel 10 could flow to a conductor,such as, for example, a metal cooking vessel resting on the surface ofregion L, and could, of course, present the possibility of an electricalshock to a housewife handling such an electrically conductive vessel aspreviously discussed. This is true if the parallel arrangement ofconductors l4 and 15 as shown in the drawings is not employed. However,if such parallel arrangement is employed, said part of the electricalleakage would flow between adjacent points on the vessel resting onsurface 11 in said region L and thus be substantially or completelycancelled out due to voltages of equal and opposite polarities appearingthroughout such region L. This effectively eliminates or cancels leakagecurrent which could otherwise flow through a housewife connected toground and in contact with said metal or electrically conductive vessel.This is, of course, similarly true throughout the lengths of conductorsl4 and 15, that is, in any substantial regions of area 12 over whichconductors l4 and 15 extend.

It is desired to here make reference to the copending United Statespatent application of Harold A. Brouneus entitled Electrical HeatingUnit, such application being filed on even date herewith and assigned tothe same assignee as the present application. Such copending applicationdiscloses another 240 volt electrical heating unit reducing thepossibility of electrical shock in a manner similar to that discussedherein but using electrical resistance conductors connected in adifferent manner across a commercial 240 volt source of alternatingcurrent.

Although there is herein shown and described only one form of anelectrical heating unit embodying the invention, it will be understoodthat various changes and modifications may be made therein within thepurview of the appended claims without departing from the spirit andscope thereof.

What is claimed is:

1. An electrical heating unit comprising;

A. a panel of a glassy material,

B. a 240 volt heating element including first and second electricalresistance conductors in physical contact with a surface of said panelin a selected area of such panel and extending over such surface infirst and second sinuous paths paralleling each other throughout thelengths thereof with the first and second ends of said first conductorbeing adjacent the second and first ends, respectively, of said secondconductor,

C. first circuit means including a first set of normally closed andthermally actuated contacts for connecting said first ends of saidconductors with each other and with one terminal of a commercial 240volt source of alternating current, and

D. second circuit means including a second set of normally closed andthermally actuated contacts for connecting said second ends of saidconductors with each other and with the opposite terminal of saidcurrent source.

2. A heating unit as in claim 1 and in which said conductors eachcomprise a narrow continuous strip of a metallic film.

3. A heating unit as in claim 1 and in which said conductors eachcomprise a narrow strip of foil.

4. A heating unit as in claim 1 and in which said glassy material is aglass-ceramic material.

5. A heating unit as in claim 2 and in which said glassy material is aglass-ceramic material.

6. A heating unit as in claim 3 and in which said glassy material is aglass-ceramic material.

1. An electrical heating unit comprising; A. a panel of a glassymaterial, B. a 240 volt heating element including first and secondelectrical resistance conductors in physical contact with a surface ofsaid panel in a selected area of such panel and extending over suchsurface in first and second sinuous paths paralleling each otherthroughout the lengths thereof with the first and second ends of saidfirst conductor being adjacent the second and first ends, respectively,of said second conductor, C. first circuit means including a first setof normally closed and thermally actuated contacts for connecting saidfirst ends of said conductors with each other and with one terminal of acommercial 240 volt source of alternating current, and D. second circuitmeans including a second set of normally closed and thermally actuatedcontacts for connecting said second ends of said conductors with eachother and with the opposite terminal of said current source.
 2. Aheating unit as in claim 1 and in which said conductors each comprise anarrow continuous strip of a metallic film.
 3. A heating unit as inclaim 1 and in which said conductors each comprise a narrow strip offoil.
 4. A heating unit as in claim 1 and in which said glassy materialis a glass-ceramic material.
 5. A heating unit as in claim 2 and inwhich said glassy material is a glass-ceramic material.
 6. A heatingunit as in claim 3 and in which said glassy material is a glass-ceramicmaterial.